EQAWarden knowledge base · Troponin I

Troponin I EQA results: why they fail and what to check.

What is known to go wrong with troponin I in external quality assurance, how each problem shows itself in the results, and the checks to make, with every source listed. This is the troponin I monograph EQAWarden ships with. First check: Confirm the method code is Atellica TnIH (high sensitivity) and compare only with that peer group.

Technical content: Craig MacKenzie, medical scientist, chemical pathology, 27 years of experience.

At a glanceKnown EQA pitfallsInvestigation checksPlainly answeredReferences
At a glance

The limits, units and methods behind every troponin I result.

RCPAQAP APS, General Serum Chemistry (GSC)±0.002 µg/L up to 0.01 µg/L, ±20% above
Unitsµg/L. 1 ng/L = 0.001 µg/L. RCPAQAP's APS is stated in µg/L; many laboratories report ng/L (x 1000).
MethodsThree-site sandwich chemiluminescent immunoassay, high sensitivity (two biotinylated monoclonal capture antibodies, mouse and sheep, on streptavidin paramagnetic particles; acridinium-labelled recombinant sheep Fab detection), direct RLU: Atellica IM TnIH (confidence: High)[1]
Contemporary (not high-sensitivity) three-site sandwich chemiluminescent assay with streptavidin capture, reporting ng/mL: Atellica IM TnI-Ultra (TnI_UL), 2017 insert, not in the 2025 assay chart (confidence: High)[3, 10]
Many other cTnI immunoassays from several manufacturers, each with its own antibodies and calibrator (confidence: High)[4, 6]
StandardisationNo JCTLM-listed reference material or procedure was found for cTnI[9]; the IFCC working group has worked towards a reference procedure and a commutable secondary material[5]. Sixteen cTnI assays differed about 10-fold on the same patient samples and between-assay variation was 29-40% before mathematical recalibration[4]. Atellica TnIH is standardised to an internal human heart homogenate standard with no WHO or NIST material named, and its IFU states results from different troponin assays are not interchangeable; the older TnI-Ultra is traceable to NIST SRM 2921[1, 3]. The fair EQA comparator is the Atellica TnIH method group.
Expected error modeMixed: proportional for calibration and lot effects; constant (absolute ng/L) near the lower limit and the 99th percentile.
Biological variationWithin-subject CV 11.09% and between-subject CV 34.38%, from the EFLM database (meta-analysis, 8 studies).
Desirable performanceImprecision 5.54%, bias 9.03%, total allowable error 18.18%, derived from biological variation (Fraser).

Platform details are for the Siemens Atellica, the platform EQAWarden's first release covers. Other platforms differ: check your own instructions for use.

Known EQA pitfalls

12 ways a troponin I result goes wrong in EQA, and how to tell them apart.

Method-group target: cardiac troponin I assays are not harmonised

Why it happens. Each cTnI method uses its own antibodies and calibrator, so the same sample gives very different numbers between methods (about 10-fold range, 29-40% between-assay variation before recalibration)[4]. An all-method or reference target for troponin I is not meaningful for a laboratory's own performance.

Direction. method-specific

How it shows. method-group, persistent; the Atellica TnIH group as a whole sits away from other method groups

Check. Compare with the Siemens Atellica TnIH peer group only; confirm that myQAP holds the high-sensitivity method code, not TnI-Ultra or ADVIA Centaur.

Confidence. High[1, 4, 5, 6]

TnIH and TnI-Ultra are different assays with 1000-fold different units

Why it happens. TnIH reports pg/mL or ng/L with a measuring interval of 2.5-25,000 ng/L and an internal heart homogenate standard; TnI-Ultra reports ng/mL (µg/L) from 0.006 to 30 µg/L and is traceable to NIST SRM 2921. A laboratory that changed assay without changing the EQA method code, or that entered ng/L where µg/L is expected, shows a step change or a factor of 1000.

Direction. either: a factor of 1000 in either direction for a unit error; method-specific for a wrong method code

How it shows. step, persistent, proportional; begins when the assay or unit changed; a ratio of exactly 1000 or 0.001

Check. Check which troponin I test definition each analyser runs, the reporting unit in CentraLink and the LIS, and the unit and method code registered with RCPAQAP.

Confidence. High[1, 3, 11]

Low-end imprecision near the 99th percentile

Why it happens. TnIH within-lab CV was 7.5% at 9.5 ng/L, 5.4% at 18.9 ng/L and 3.9% at 39 ng/L; the 99th percentile is about 45 ng/L with CV below 10%; LoQ 2.5 ng/L (CV 20%)[1]. An independent multicentre study found within-lab CV 1.8-7.6% from 10 ng/L upwards[8]. The IFCC task force defines a high-sensitivity assay by CV of 10% or less at the 99th percentile and measurable values in at least half of healthy men and women[6, 7]. An EQA sample near the decision limits carries an absolute SD of about 1 ng/L, which is a large percentage at low values.

Direction. either

How it shows. concentration-dependent, constant, single; deviations mainly on the low sample and of a fixed size in ng/L

Check. Judge a low sample against the APS absolute limit; compare with low-level IQC SD; regress the cycle's results on targets to separate constant from proportional error.

Confidence. High[1, 8, 6, 7]

New reagent lot and its master curve (TnIH)

Why it happens. Each Atellica IM reagent lot carries a lot-specific master curve read from 2D barcodes; a new lot needs a new two-point calibration. Intervals in the IFU: lot calibration 47 days, pack calibration 31 days, onboard stability 28 days. The TnIH master curve material (5 levels) checks calibration across the range; its values are assigned on the same system. A lot-to-lot difference that the two-point calibration does not correct shifts results on every analyser using that lot. The size of the shift can differ between patient samples and EQA or control material.

Direction. either (sign set by the lot difference)

How it shows. step, proportional, persistent; begins at the date the new reagent lot was first used and follows that lot

Check. Pull the reagent and calibrator lot history for the analysis date; compare IQC before and after the lot change and, if available, run the master curve material or a retained EQA sample on both lots.

Confidence. High[1, 12, 13, 2]

Two-point recalibration or calibrator handling (TnIH, kit CAL L and CAL H)

Why it happens. Atellica IM two-point calibration adjusts the lot master curve with a low and a high calibrator. The low calibrator is liquid; the high calibrator is lyophilised and needs exactly 1.00 mL special reagent water (class A pipette, 15-20 minutes). Both are usable for only 4 hours once opened or reconstituted (2-8 C or on board); frozen aliquots keep 30 days with one thaw, and kit calibrators may only be used with reagent of the same kit lot. A reconstitution volume error, an evaporated or out-of-date opened calibrator, or a calibrator from the wrong lot shifts every result after that calibration on that analyser. The 4 hour limit is unusually short, so a calibration run late with calibrator left from an earlier session is a realistic cause of a dated shift.

Direction. either

How it shows. step, proportional, instrument-specific; starts at a dated calibration on one analyser

Check. Open the calibration record for the run (date, calibrator lot, reconstitution or opening date and time, calibration acceptance); compare IQC before and after; compare with a second analyser calibrated separately.

Confidence. High[1, 12]

Commutability and troponin forms in the EQA material

Why it happens. Troponin circulates as complexes and fragments, and processed EQA material may contain cTnI in forms that antibodies recognise differently; this spreads method groups in a sample-specific way. Pooled and EQA materials behaved like patient samples in most cTnI assays in two harmonisation studies, but a few samples showed large assay-specific differences[4, 14, 15].

Direction. method-specific

How it shows. sample-specific, method-group; one sample shows a larger spread between method groups than the next

Check. Look at whether the spread between method groups is larger for this sample than for the other; if the whole Atellica group moved on one sample only, treat it as a material effect.

Confidence. Medium[4, 14, 15, 16]

Standing time after reconstitution

Why it happens. The TnIH IFU allows capped samples 8 hours at room temperature and 24 hours at 2-8 C, and frozen storage with one freeze only. Reconstituted EQA material left longer, or refrozen, is outside these limits; the effect on lyophilised material is not published.

Direction. unknown (a loss would read negative)

How it shows. single, sample-specific, drift

Check. Record the reconstitution and analysis times; if a rerun was made the next day, compare the two results.

Confidence. Low[1, 17]

Chemiluminescent signal or wash fault in a sandwich assay

Why it happens. The assay is a two-site sandwich with a direct relationship between analyte and relative light units (RLU). A loss of signal (trigger reagents, luminometer, particle loss at washing) reads low, while poor washing of unbound label reads high; competitive assays on the same analyser move the opposite way. TnIH uses Atellica IM Wash and the APW3 probe wash (onboard 28 days).

Direction. either: negative for a loss of signal; positive for residual unbound label

How it shows. instrument-specific, survey-wide, analyte-group:im_sandwich; sandwich assays move one way and competitive assays the other on the same analyser

Check. Check whether other Atellica IM sandwich assays on the same analyser moved in the same direction and competitive assays in the opposite direction; review trigger reagent, wash fluid and probe wash onboard times, luminometer checks and maintenance logs.

Confidence. Medium[1, 12, 18, 10]

High-dose hook effect (sandwich format)

Why it happens. Two-site sandwich assays can under-read at extreme concentrations when the antibodies are saturated. The IFU reports no falsely low result up to 500,000 ng/L (such samples still report above 25,000 ng/L). Only samples above 25,000 ng/L may be diluted (1:2 or 1:5 with Multi-Diluent 11). EQA materials are normally made far below that.

Direction. negative (only above the tested hook-free range)

How it shows. single, concentration-dependent; only a sample whose true value exceeds the tested hook-free range

Check. A low result on a very high EQA sample is more likely a dilution or result-path error than a hook: check the dilution factor, auto-dilution flags and whether the result was above range before dilution; if a hook is suspected, rerun at 1:10 or 1:100.

Confidence. High[1, 19, 20]

Haemolysis and biotin

Why it happens. TnIH changed 10% or less up to haemoglobin 500 mg/dL and biotin 3500 ng/mL[1]; an independent evaluation found a slight bias at haemoglobin 5.0 g/L with cTnI 50 ng/L[8], and Atellica met its claims in a nine-assay study[21]. The older TnI-Ultra is biotin sensitive (about 10% low above 10 ng/mL biotin)[3]. Biotin is a patient issue and unlikely in EQA material.

Direction. unknown for haemolysis on TnIH; negative for biotin on TnI-Ultra

How it shows. single, sample-specific

Check. Inspect the vial for haemolysis; for a TnI-Ultra user, note the biotin sensitivity only if the material is known to contain biotin.

Confidence. Low[1, 3, 8, 21]

Test definition update left operator-defined parameters unchanged

Why it happens. Siemens issues new Atellica IM test definition versions (TnIH test definition 1.3 added alternate units with a default conversion factor (pg/mL to ng/L is 1:1)). Operator-defined parameters are not updated automatically when a test definition is installed, so a dilution point, unit or conversion factor set by the laboratory can differ from the new default.

Direction. either

How it shows. step, instrument-specific; starts at the software or test definition update

Check. Compare the installed test definition version, reporting unit and conversion factor on each analyser with the current assay chart and the enhancement notice; check the date of the last test definition installation.

Confidence. Medium[1, 11, 10]

Heterophile or human anti-animal antibodies

Why it happens. The IFU says the assay is designed to minimise heterophilic antibody interference but that such antibodies can still give falsely high or low results. The IFU also warns that cTnI autoantibodies with high gamma globulin can depress results in individual patients. These antibodies belong to individual donors; a pooled EQA material is unlikely to carry them at an effective level unless it comes from a single donor.

Direction. either

How it shows. single, sample-specific; one sample reads off in one method group and not in others

Check. If a single-donor EQA sample is off in the Atellica group only, ask RCPAQAP about the material source; retest after a heterophile blocking step or on another platform if the laboratory keeps the sample.

Confidence. Low[1, 22, 23]

Investigation checks

The checks, in order.

  1. Confirm the method code is Atellica TnIH (high sensitivity) and compare only with that peer group.
  2. Check the unit path: TnIH reports ng/L; RCPAQAP's APS is stated in µg/L (a ratio of 1000 is a unit error).
  3. For a low sample, judge the absolute difference in ng/L against low-level IQC SD and the APS absolute limit.
  4. Check the calibration record: calibrators are usable for only 4 hours once opened; lot 47, pack 31 days.
  5. If several IM sandwich assays on one analyser moved together, review trigger, wash and luminometer records.
  6. If only one sample is off and the Atellica group moved too, treat it as a material effect.

Unit traps

  • TnIH reports ng/L (= pg/mL); RCPAQAP's APS is stated in µg/L; µg/L x 1000 = ng/L.
  • TnI-Ultra reports ng/mL (= µg/L): switching between TnI-Ultra and TnIH changes the number 1000-fold.

EQAWarden runs these checks as rules on every survey, ranks the likely causes with their evidence, and the reviewer decides. All analytes · The 58 rules · The whole knowledge base · How an EQA investigation runs

Plainly answered

Questions about troponin I EQA.

What is the RCPAQAP allowable performance specification for troponin I?

In the General Serum Chemistry (GSC) programme it is ±0.002 µg/L up to 0.01 µg/L, ±20% above, evaluated at the target. RCPAQAP can change its specifications, so confirm the current table at each enrolment year.

What is a common cause of a failed troponin I EQA result?

Method-group target: cardiac troponin I assays are not harmonised. Each cTnI method uses its own antibodies and calibrator, so the same sample gives very different numbers between methods (about 10-fold range, 29-40% between-assay variation before recalibration). An all-method or reference target for troponin I is not meaningful for a laboratory's own performance.

What should be checked first when a troponin I EQA result fails?

Confirm the method code is Atellica TnIH (high sensitivity) and compare only with that peer group.

How are troponin I units converted?

1 ng/L = 0.001 µg/L.

References

Where every fact on this page came from.

  1. Siemens Healthineers. Atellica IM High-Sensitivity Troponin I (TnIH) [OUS-Plus], Instructions for Use, part 11208873 Rev. 11, 2025-04. Siemens Document Library id 1114154.
  2. Siemens Healthineers. Atellica IM High-Sensitivity Troponin I Master Curve Material (TnIH MCM), Instructions for Use, part 11200074 Rev. 03, 2022-04. Siemens Document Library id 884456.
  3. Siemens Healthineers. Atellica IM Troponin I Ultra (TnI-Ultra) [OUS], Instructions for Use, part 10995428 Rev. 02, 2017-11. Siemens Document Library id 389979.
  4. Tate JR, Bunk DM, Christenson RH, et al.; IFCC Working Group on Standardization of Cardiac Troponin I. Evaluation of standardization capability of current cardiac troponin I assays by a correlation study: results of an IFCC pilot project. Clin Chem Lab Med 2015;53:677-690. Sixteen cTnI assays on 79 patient samples: about 10-fold difference lowest to highest; mathematical recalibration cut between-assay variation from 40% to 22% (low), 37% to 20% (medium) and 29% to 14% (high concentration).
  5. Tate JR, Bunk DM, Christenson RH, Katrukha A, Noble JE, Porter RA, Schimmel H, Wang L, Panteghini M. Standardisation of cardiac troponin I measurement: past and present. Pathology 2010;42:402-408.
  6. Apple FS, Sandoval Y, Jaffe AS, Ordonez-Llanos J; IFCC Task Force on Clinical Applications of Cardiac Bio-Markers. Cardiac troponin assays: guide to understanding analytical characteristics and their impact on clinical care. Clin Chem 2017;63:73-81. doi:10.1373/clinchem.2016.255109
  7. Wu AHB, Christenson RH, Greene DN, Jaffe AS, Kavsak PA, Ordonez-Llanos J, Apple FS. Clinical laboratory practice recommendations for the use of cardiac troponin in acute coronary syndrome: expert opinion from the Academy of the American Association for Clinical Chemistry and the Task Force on Clinical Applications of Cardiac Bio-Markers of the IFCC. Clin Chem 2018;64:645-655.
  8. Buno Soto A, Peoc'h K, Fasano T, et al. Performance evaluation of the high sensitive troponin I assay on the Atellica IM analyser. Biochem Med (Zagreb) 2022;32:020709. Multicentre: repeatability CV 1.1-4.7%, within-lab CV 1.8-7.6% (10-25,000 ng/L); LoB, LoD and LoQ agreed with 0.5, 1.6 and 2.5 ng/L; no biotin interference to 1500 µg/L; slight bias at haemoglobin 5.0 g/L with cTnI 50 ng/L.
  9. JCTLM Database of higher-order reference materials and reference measurement procedures. Keyword searches (troponin, troponin I, cardiac troponin, ferritin, prostate, PSA, natriuretic, BNP) through the public API https://www.jctlmdb.org/backend/api/jctlm/searchRm and searchRmp (multipart fields page_number, nb_results, keywords), 2026-09-29. Found only C1RM_P4, BCR-613 prostate specific antigen (purified PSA, EU-JRC, certified mass 70.8 ug per unit); none found for troponin I or T, ferritin, BNP or NT-proBNP. Absence in a keyword search is reported as 'none found', not as proof of non-listing.
  10. Siemens Healthineers. Atellica Solution IM Assay Chart, part 11314389 Rev. 05, 2025-12. Siemens Document Library id 1151608. https://content.doclib.siemens-healthineers.com/rest/v1/view?document-id=1151608
  11. Siemens Healthineers. Atellica IM Analyzer Test Definition Enhancements, Customer Information, part 11314997 Rev. 17, 2026-05. Siemens Document Library id 1173692. https://content.doclib.siemens-healthineers.com/rest/v1/view?document-id=1173692
  12. Siemens Healthineers. Atellica Solution Operator's Guide, software version 1.31, part 11069101 Rev. 13, 2025-10.
  13. Miller WG, Erek A, Cunningham TD, Oladipo O, Scott MG, Johnson RE. Commutability limitations influence quality control results with different reagent lots. Clin Chem 2011;57:76-83. doi:10.1373/clinchem.2010.148106
  14. Clerico A, Ripoli A, Masotti S, et al. Pilot study on harmonization of cardiac troponin I immunoassays using patients and quality control plasma samples. Clin Chim Acta 2016;456:42-48. EQA control samples and plasma pools fell within the 95% prediction intervals of patient-sample regressions for four cTnI methods.
  15. Zhang et al. Commutability of possible external quality assessment materials for cardiac troponin measurement. PLoS One 2014 (first-author initial and page details not confirmed). https://pmc.ncbi.nlm.nih.gov/articles/PMC4085021/
  16. Badrick T, Miller WG, Panteghini M, Delatour V, Berghall H, MacKenzie F, Jones G. Interpreting EQA - understanding why commutability of materials matters. Clin Chem 2022;68:494-500. doi:10.1093/clinchem/hvac002
  17. RCPAQAP Chemical Pathology. QAP Commutability & Matrix Effects. 2013 (Wayback capture, 2014-2015 range; base URL not captured in the research document).
  18. Wild D (ed.). The Immunoassay Handbook: Theory and Applications of Enzyme Immunoassay, Electrochemiluminescence and Related Techniques. 4th ed. Oxford: Elsevier; 2013. Cited as textbook knowledge for competitive versus sandwich signal-response relationships; not re-read in this review.
  19. Jassam N, Jones CM, Briscoe T, Horner JH. The hook effect: a need for constant vigilance. Ann Clin Biochem 2006;43:314-317. doi:10.1258/000456306777695726
  20. Dodig S. Interferences in quantitative immunochemical methods. Biochem Med (Zagreb) 2009;19:50-62. doi:10.11613/BM.2009.005
  21. Harley K, Bissonnette S, Inzitari R, Schulz K, Apple FS, Kavsak PA, Gunsolus IL. Independent and combined effects of biotin and hemolysis on high-sensitivity cardiac troponin assays. Clin Chem Lab Med 2021;59:1431-1443. Nine hs-cTn assays including Siemens Atellica; the Roche Elecsys Troponin T-hs assays read falsely low with in vitro haemolysis at 0-3 g/L free haemoglobin (up to 3 ng/L or 13%) and with biotin; Atellica met its claims.
  22. Kricka LJ. Human anti-animal antibody interferences in immunological assays. Clin Chem 1999;45:942-956. doi:10.1093/clinchem/45.7.942
  23. Tate J, Ward G. Interferences in immunoassay. Clin Biochem Rev 2004;25:105-120 (AACB journal). https://pmc.ncbi.nlm.nih.gov/articles/PMC1904417/
  24. EFLM Biological Variation Database (Aarsand AK et al., EFLM WG-BV). https://biologicalvariation.eu/ - meta-analysis values read from https://biologicalvariation.eu/api/meta_calculations and individual studies from https://biologicalvariation.eu/api/bv_specifications, retrieved 2026-09-28. https://biologicalvariation.eu/
  25. Fraser CG. Biological Variation: From Principles to Practice. Washington DC: AACC Press; 2001 (textbook; formulae desirable CVa<=0.5CVi, bias<=0.25*sqrt(CVi^2+CVg^2), TEa=1.65*CVa+bias).
  26. RCPAQAP. Chemical Pathology Analytical Performance Specifications (web page; dateModified 2025-03-05). https://rcpaqap.com.au/resources/chemical-pathology-analytical-performance-specifications/

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